This development relates generally to a web inspection method and apparatus using an improved lighting and camera arrangement. It is described herein with reference to a web inspection method and apparatus for a flexible imaging web such as, e.g., a photoreceptor web used to manufacture photoreceptor belts for electrophotographic imaging systems, but it is not intended to be limited to inspection on any particular type of web material.
In the art of electrophotography, an electrophotographic member comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the imaging surface of the photoconductive insulating layer. The member is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated area. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
The electrophotographic member is often in the form of a flexible multilayered photoreceptor belt comprising a substrate, a conductive layer, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, and a charge transport layer and, in some embodiments, an anti-curl backing layer.
As more advanced, higher speed electrophotographic copiers, duplicators and printers have been developed, the electrical and mechanical performance requirements for photoreceptor belts have become more demanding. New digital color and other image-producing products cannot tolerate defects that have been acceptable for previous generation imaging apparatus, such as analog or “light-lens” copiers.
These heightened electrical and mechanical performance requirements are not met when certain defects are located on the surface of or within one or more of the layers of the multilayered belt photoreceptors. These defects are caused by the presence of dirt particles on the substrate, conductive layer, optional hole blocking layer, optional adhesive layer, charge generating layer, charge transport layer and/or optional anti-curl backing layer. Thus for example, particles of dirt (particulate debris) residing on an uncoated or coated substrate surface during application of coatings to form an electrostatographic imaging member, such as a photoreceptor, can cause bubbles or voids to form in the various applied coating layers. It is believed that the dirt particles behave in a manner similar to a boiling chip that initiates solvent boiling at the location of the particle. This local boiling problem is aggravated when a coating solution is maintained near the boiling point of the coating solvent during deposition of the coating or during drying. The formation of bubbles in a coating is particularly acute in photoreceptor charge generation layer coatings and in charge transport layer coatings. Also, dirt particles tend to trap air during application of a coating and the trapped air expands during drying to form an undesirable bubble in the coating. Further, any dirt particles residing on one or both surfaces of an electrophotographic imaging member web substrate or coating thereon can adversely affect adjacent surfaces when the web is rolled up into a roll because the dirt particles cause impressions on the adjacent web surfaces. Because these undesirable impressions can be repeated through more than one overlapping web layer, large sections of a coated web must be scrapped, and this result is highly undesirable.
It should be apparent from the foregoing that it is highly desirable to identify defects in a photoreceptor web before the web is cut and formed into an endless imaging belt. If the defects are identified in advance, it is often possible to cull the defective region from the web so that same does not form part of a finished photoreceptor belt, or to ensure that the defective part of the web is used to manufacture a photoreceptor belt usable for an application where the defect(s) will have no undesired consequences.
It is known to use human inspectors alone or in combination with automated web inspection system in an effort to identify web defects. In one known system, a human operator visually inspects the translucent web as it passes over a light-box. In another embodiment, machine-vision systems are used to acquire images of web moving therepast, and these images are processed according to defect-identification algorithms in an effort to provide an automated web inspection method and apparatus. In known systems of this type, reflected light images and transmitted light images are acquired sequentially and not simultaneously. As such, with conventional web inspection schemes, it is not possible to perform real-time acquisition and analysis of combined transmitted/reflected light images. With conventional system, the sequentially acquired images must be combined off-line, and then processed for image identification and classification. Obviously, this is highly undesired, especially in a process where defects in the web are marked immediately downstream from the inspection process and/or in a process where the web is cut for into sections to be formed into end-products, e.g., photoreceptor belts, immediately downstream from the inspection process.
In light of the foregoing issues, it has been deemed desirable to provide a real-time web inspection method and apparatus using combined reflected and transmitted light images as disclosed herein.